On a recent Air Canada flight from Chile to Toronto, 6'2 Colin Savage says he was forced to stay in his economy class seat for most of the 10-hour flight due to turbulence. After returning to his home in Victoria, British Columbia, Savage visited a doctor because of "horrible" pain in his lower back. Savage was then told he had deep vein thrombosis (DVT), which can occur when travelers stay in a small, cramped space—usually for more than four hours—with little or no movement. According to Savage, resulting blood clots traveled from his leg, through his heart, and into his lungs. Doctors at the hospital told him he had nearly lost his life, reports Canada's CBC News.

For their part, Air Canada responded to Savage's complaint by noting that there is no conclusive medical evidence linking flying specifically to being the sole cause of DVT; instead, they said DVT is actually the result of pre-existing medical conditions. This is mostly true: The World Health Organization reports that prolonged periods of immobility on long-distance travel, whether by car, bus, train, or air, all pose similar risks for DVT. According to the American Society of Hematology, risk factors include pregnancy, recent surgery or trauma, obesity, and inherited blood-clotting abnormalities. In the U.S., it is estimated that 900,000 people annually are affected by DVT and resulting pulmonary embolisms (PE), and up to 100,000 die from it.

And while the longer the flight, the more at risk you are for developing a clot, there are some precautions you can take to minimize your risk: Stay hydrated. Wear loose, comfortable clothing and when you're seated in the air, walk around once an hour to get the blood moving. Can't get up? Stretch your legs by flexing and relaxing your calf muscles and feet; rolling your ankles; and clenching and spreading out your toes, all of which can help circulation.